B7.013 Prework 2: Nerve Conduction Studies & EMG Flashcards
which nerves can be tested on nerve conduction studies
large, myelinated nerves
small ones get buried in the signal, so abnormalities are not measurable
normal nerve conduction velocity
50-60 m/s
112 mph
function of motor nerve conduction studies
studies MOTOR nerve conduction, read off of the muscle
2 stimulation points, and calculate distance/time between the two points
amplitude = number of nerves
latency = speed of action potential
function of sensory nerve conduction studies
read off of the nerve itself
more challenging due to much lower amplitude than motor nerves
appearance of myelinopathy on NCS
relatively preserved amplitude of response
very slow velocities, long latencies, conduction block
appearance of axonopathy on NCS
low amplitude responses
relatively preserved velocity
how do sensory nerve APs appear in radiculopathies
NORMAL
patient will be numb, but if lesion is proximal to the dorsal root ganglion, the sensory nerve will continue to function appropriately bc the nucleus keeps the nerve alive
M wave
direct activation of motor axons and muscles due to stimulation by NCS
F wave
recurrent excitation of motoneuron due to retrograde depolarization of AP toward spinal cord and then back to the periphery
H reflex
deep tendon like reflex on NCS
what is a motor unit
motor neuron in spinal cord + peripheral nerve + associated muscle fibers
fibrillation
spontaneously firing muscle fiber (acute denervation)
fasciculation
a spontaneously firing motor unit
appearance of chronic denervation / reinnervation on EMG
lots of random, asymmetric firings
large, wide, complex motor units
when do EMGs have poor sensitivity
early disease
mild disease
focal neuropathies (best one is median, but better with diffuse lesions overall)
small fiber neuropathies
